拉萨地体西部左左乡地区中新世石英二长岩锆石U-Pb年龄和岩石成因及构造模式  

Zircon U-Pb age,petrogenesis and tectonic model of Miocene quartz monzonite in Zuozuoxiang area,Western Lhasa terrane

作　　者：张博川 范建军[1,2] 罗安波 李航 申迪 刘海永 ZHANG Bochuan;FAN Jianjun;LUO Anbo;LI Hang;SHEN Di;LIU Haiyong(College of Earth Science,Jilin University,Changchun 130061,Jilin,China;Key laboratory of Mineral Resources Evaluation in Northeast Asia,Ministry of Land and Resources,Changchun 130061,Jilin,China;Tibet Institute of Geological Survey,Lhasa 850000,Tibet,China)

机构地区：[1]吉林大学地球科学学院,吉林长春130061 [2]东北亚矿产资源评价自然资源部重点实验室,吉林长春130061 [3]西藏自治区地质调查院,西藏拉萨850000

出　　处：《地质通报》2022年第8期1358-1368,共11页Geological Bulletin of China

基　　金：第二次青藏高原综合科学考察研究项目《典型地区岩石圈组成、演化与深部过程专题》(编号:2019QZKK0702)、《特提斯大陆增生与第三极形成》(编号:2019QZKK0703);国家自然科学基金项目《班公湖-怒江缝合带早白垩世洋岛型岩石组合构造属性研究——以仲岗和塔仁本为例》(批准号:41972236)。

摘　　要：中新世的岩浆活动对于判别青藏高原新生代的构造演化具有重要意义,本文在拉萨地体西部左左乡地区新厘定出一套中新世石英二长岩。通过LA-ICP-MS测年,获得锆石^(206)Pb/^(238)U年龄为22.38±0.46 Ma(n=13,MSWD=0.71),此年龄可代表石英二长岩的形成时代。全岩化学成分显示,其具有高的SiO_(2)(65.87%~66.90%)、K_(2)O(6.19%~6.41%)含量、K_(2)O/Na_(2)O值(1.7~1.8)及低的MgO(1.71%~1.76%)含量,岩石类型属于拉萨地体中新世钾质中酸性岩系列。依据岩石高的Mg^(#)(56.5~57.8)值、Nb/Ta(16.0~16.4)值、Cr(46.0×10^(-6)~48.9×10^(-6))、Ni(32.6×10^(-6)~34.8×10^(-6))含量及大量的暗色包体,推测左左乡中新世石英二长岩形成于壳源岩浆与幔源岩浆的混合。依据区域内的隆升研究结果,推测印度板片分段俯冲及撕裂模型相比于岩石圈地幔对流减薄模型、增厚岩石圈拆沉模型、俯冲印度板片断裂模型能够更合理地解释拉萨地体中新世钾质-超钾质火山岩的成因。The Miocene magmatism is of great significance to distinguish the Cenozoic tectonic evolution of the Tibetan Plateau.In this paper,a new set of Miocene quartz monzonite has been redefined in Zuozuoxiang area,western Lhasa terrane.Zircon U-Pb dating shows that the age of quartz monzonite is 22.38±0.46 Ma.Whole rock geochemical test shows that quartz monzonite has high SiO_(2)(65.87%~66.90%),K_(2)O(6.19%~6.41%)contents,K_(2)O/Na_(2)O(1.7~1.8)ratios and low MgO(1.71%~1.76%)contents,belonging to potassic intermediate-acid rock.According to the high Mg^(#)(56.5~57.8),Nb/Ta(16.0~16.4),Cr(46.0×10^(-6)~48.9×10^(-6)),Ni(32.6×10^(-6)~34.8×10^(-6))and a large number of dark inclusions in the rocks,we believe that Miocene quartz monzonite from Zuozuoxiang area was formed by partial melting of thickened lower crust with the addition of mantle material.In addition,based on the results of uplift studies,we believe that the tearing of Indian plate is more suitable for the interpretation of Miocene potassic-ultrapotassic rocks in Lhasa terrane than the convective thinning of lithospheric mantle,the delamination of thickened lithosphere and the break-off of Indian plate.

关 键 词：拉萨地体 中新世 钾质中酸性岩 印度板片撕裂 LA-ICP-MS锆石U-PB测年 

分 类 号：P534.621[天文地球—古生物学与地层学] P597[天文地球—地质学] P588.12